Methylbiphenyl compounds are useful intermediates in the production of a variety of commercially valuable products, including polyesters and plasticizers for PVC and other polymer compositions. For example, they can be converted to an ester plasticizer by a process comprising oxidation to produce the corresponding mono- or dicarboxylic acid followed by esterification of the acid function with a long chain alcohol. In addition, diphenyl-4,4′-dicarboxylic acid, optionally together with diphenyl-3,4′-dicarboxylic acid, is a potential precursor, either alone or as a modifier for polyethylene terephthalate (PET), in the production of polyester fibers, engineering plastics, liquid crystal polymers for electronic and mechanical devices, and films with high heat resistance and strength.
As disclosed in our co-pending U.S. patent application Ser. Nos. 14/201,287 and 14/201,224, both filed Mar. 7, 2014 and incorporated herein by reference, dimethylbiphenyl compounds may be produced by hydroalkylation of toluene followed by dehydrogenation of the resulting (methylcyclohexyl)toluene (MCHT). An alternative route via benzene is described in our co-pending U.S. patent application Ser. No. 14/164,889, filed Jan. 27, 2014 and also incorporated herein by reference. In this alternative route, the benzene is initially hydroalkylated to cyclohexylbenzene (CHB), which is then dehydrogenated to biphenyl. The biphenyl is subsequently alkylated with methanol to produce the desired methylbiphenyl compounds.
One problem with both of these routes for producing methylbiphenyl compounds is that the catalyst employed in the dehydrogenation step tends to undergo rapid deactivation. There is therefore interest in developing an improved dehydrogenation catalyst that exhibits enhanced stability when employed in the dehydrogenation of MCHT and and/or CHB.